The present invention relates to exhaust manifolds for internal combustion engines and the like, and in particular to a hybrid clamshell construction and method therefor.
Exhaust manifolds for internal combustion engines are well known in the art, and serve to direct the flow of exhaust gases from the engine heads or exhaust ports to the atmosphere through an exhaust system, which may include catalytic converters, mufflers, tailpipes and the like. Since exhaust manifolds are exposed to extremely high temperatures during operation, and experience temperature fluctuations during use, they typically have a very heavy-duty, one-piece, cast iron construction. Different portions of the exhaust manifold are subjected to a variety of different temperatures, depending upon their proximity to the engine head or exhaust port, exhaust back pressure in the system, manifold wall thickness, and other dynamics of the flow of exhaust gases through the manifold. These localized temperature gradients, and the geometry of the manifold, generate substantial stress and strain within the manifold itself, which must be considered during the design of the manifold to ensure sufficient durability and efficient exhaust gas flow. The cycling of the manifold between extremely hot operating temperatures and cool ambient temperatures can also result in thermal fatigue which weakens the manifold, and can adversely impact the engine exhaust gas dynamics, as well as engine efficiency itself.